Most antiques will lose some of their value after being restored . There are some exceptions . It really depends on how bad of condition the Item is in . Painting value can be increased with cleaning , it really depends on if the item has some greater historical associaton and, what kind of Value it actually has in that particular area. Restorations are a tricky field , Has a lot to do on how well it is done.
Guns are another story , once you lose the original patina / finish it hurts value . Japanese swords are an exception . They are one of the better antiques that actually gain value after restoration . repairing 2 strands of beads with the original beads would not adversly affect the Value . If you had to replace some major pieces , I believe would hurt the value . ........ Bubba